Development and Demonstration of a New Method of Physical Weed Control

Development and Demonstration of a New Method of Physical Weed Control

Summary

New tools for controlling weeds would be useful for soybean and corn production in organic systems or in systems in which weeds developed resistance to multiple herbicides. Here we report on two developments during 2012: (i) the safety to soybean seedlings of using air-propelled abrasive grit (PAG) for managing weeds, and (ii) fabrication of a four-row implement that uses PAG to manage weeds (PAGMan).
PAG performs well for in-row weed control in corn, but crop safety in soybean is unknown. We found that soybean is sensitive to PAG only at the VC (cotyledon) stage of seedling development. Other stages appear insensitive to PAG.
Construction of PAGMan was completed in spring and fine-tuned during the summer of 2012. The implement delivers about 300 kg of grit per hectare (about 300 lbs/A). Delivery rates vary according to tractor speed and a host of optional settings on the implement. Distribution of grit emission rates across the implement’s eight nozzles is highly uniform. Appreciable field-testing of the implement will occur in 2013.

Objectives/Performance Targets

Our objectives were two-fold. The first was to examine the tolerance of soybean seedlings to abrasive grit. We were concerned that abrasive grit may damage soybean in the same manner as it does small weed seedlings. We hypothesized that the growth stage at which soybean seedlings were exposed to grit may be associated with differential sensitivity.

The second objective was to complete construction of a tractor-mounted, PTO-driven, four-row abrasive grit applicator and test the implement in field settings.

Accomplishments/Milestones

Milestone 1: We examined responses to abrasion by corn-cob grit of soybean seedlings at VE, VC, VU, V1, V2, and combinations of these growth stages in both greenhouse and field settings. Seedling leaf areas and dry weights in greenhouse experiments were reduced by treatments that included abrasion at VC, with the primary effect expressed through reductions in the size of the unifoliate leaf. In the field, soybean stand also was reduced by grit applications at VC, especially if followed by a second application at VU or V1. However, soybean yield was not reduced by grit applied at any soybean stage of growth. End-of-season weed dry weights did not differ from hand-weeded checks and did not impact soybean yields. Thus, abrasive grit for in-row weed control can be applied at least twice at VE through V2 growth stages without lowering soybean yield, but applications at VC probably should be avoided.

Milestone 2: PAGMan is an implement that was designed, constructed, and fine-tuned at the Agricultural and Biosystems Engineering Department at South Dakota State University during winter through summer 2012. It is a tractor-mounted implement with a PTO-driven air compressor that delivers PAG at adjustable pressures through four pairs of nozzles aimed at either side of the bases of crop rows. The abraded swath resulting from each nozzle is about 5 to 10 cm wide, which creates a 10 to 20 cm-wide band of shredded weed seedlings centered on the crop row. At typical implement settings, PAGMan delivers about 84 ± 5.2 g per sec of grit. At the slowest conceivable operational speed of 1 m per second, this rate equates to 275 kg grit per hectare. Two to three abrasion events are needed for season-long control of annual weeds, thus 500 to 1000 kg per hectare of grit likely will be required. Much additional testing of PAGMan is necessary to verify its utility.

Impacts and Contributions/Outcomes

1. PAGMan demonstrated at the Crop & Soil Field Day of the University of Minnesota’s West Central Research and Outreach Center, July 2012.

2. PAGMan demonstrated at the annual USDA-ARS Field Day, Swan Lake Research Farm, Stevens County, MN, August 2012.

3. The following formal presentation was made:
Forcella, F., S. Clay, and D. Humburg. 2012. Field Application of Abrasive Grit for Postemergecne Weed Control in Corn and Soybean. Annual meeting of the Weed Science Society of America, paper #279.

4. PAGMan elicited articles during 2012 in the Morris Tribune (local newspaper, August), Minnesota Public Radio (May), and Furrow Magazine (European edition, June).

5. The following article was published:
Forcella, F. 2012. Air-propelled abrasive grit for postemergence weed control in field corn. Weed Technology 26: 161-164.

6. The following manuscript was submitted for publication:
Forcella, F. (submitted) Soybean seedlings tolerate abrasion from air-propelled grit. Weed Technology

• Photo of abrasive grit applicators
• Weed Technology article (assessment in field corn)
• Video of abrasive grit applicator at USDA-ARS Field Day (August 2012)

Collaborators: